Can you lose a kingdom's tribute?

I just noticed I am down to 9 tribute, and I was receiving 11. Does upgrading a kingdom’s level have anything to do with it which I just did?

Every time when you collect tribute, it rolls a tribute chance for each kingdom separately, so the actual number varies - sometimes 10 kingdoms roll YES, sometimes 15 do, other times 25 or whatever.

Upgrading a kingdom increases chance of that particular kingdom rolling YES when you collect tribute.
Just browse though kingdom level/power level tabs to see at what upgrade levels what happens.